1. Field of Invention
The present invention relates generally to a method for treating waste cellulosic fiber and paper mill sludge and, more particularly, to a continuous flow process for treating waste cellulosic fiber and paper mill sludge in an energy and time saving manner to obtain an environmentally safe material for use in a variety of applications.
2. Background
It is well known that waste cellulosic fiber and paper mill sludge, which are produced in large quantities in most industrial nations of the world today due to the large usage of paper, constitute one of our most serious environmental problems. Paper mill sludge has substantially little usage as a material that can be employed in other industrial applications. Because of its non-utility, the paper mill sludge is merely discarded, along with other waste cellulosic fiber, creating a tremendous disposal problem.
Some have attempted to find a useful purpose for such waste cellulosic fiber and paper mill sludge. In particular, U.S. Pat. No. 4,799,961 to Friberg discloses the use of pulped paper or waste material from paper mills as part of a process for forming cementious fiber impregnated constructions compositions. But the Friberg process has certain limitations that make its commercial application of questionable feasibility.
There are three basic reactionary steps in Friberg. The first is boiling a slurry of calcium oxide and siliceous material. Friberg boils this first intermediate mixture for a period of at least two hours. After boiling, Friberg must allow the mixture to stand for 3 to 5 days or more. The second step is ball milling calcium chloride, calcium oxide, calcium sulfate, iron oxide, diatomite, and portland cement to obtain a second intermediate mixture. The third step is blending the results of the first two steps to a thick paste in which portland cement, further siliceous material, fiber and other additives are mixed--other additives being up to 80% of the mixture. Friberg also dries his end product to about a 15% moisture content.
The main drawback to Friberg's method is that it is a batch process as opposed to a continuous flow process. This hampers the implementation of Friberg's process on a large scale. Further, the reactionary steps in Friberg's process require significant energy expenditures and time commitments. For instance, his boiling of his first intermediate mixture for a period of at least two hours, while not a significant expense in the context of a small batch, becomes commercially significant when a 300 ton per day fiber production run is anticipated. Still further, Friberg must allow his first intermediate mixture to stand for three to five days or more. Again, considering a 300 ton per day production run, a production rate similar to the manufacture of plywood, tile or brick, the amount of space required for storage of the intermediate mixtures is tremendous.
Another issue not addressed by Friberg is the treatment of toxic chemicals and elements contained within waste cellulosic fiber and paper mill sludge. These products typically contain dioxins which are a major source of toxic contamination of soils and water supplies. "Dioxins" as used herein means all toxic or carcinogenic substances carried by acidic water in paper mill waste sludge, including phenols, heavy metals and compounds of heavy metals.
Dioxins are suspected of causing cancer and birth defects. From the beginning of the industrial age, large quantities of materials containing dioxins have been dumped, either accidentally or deliberately, in a heretofore entirely reckless fashion. Consequently, material containing dioxins is a significant hazard to the environment. The disposal of all materials containing dioxins, and particularly paper mill sludge, has caused great concern. Incineration has been employed as a means of disposal and land burial has been the other primarily practiced method of disposal of waste cellulosic fiber and paper mill sludge. When the material is buried there always remains a possibility of the dioxins being leached out and carried into drinking water or otherwise providing a contaminant to the environment. This invention is also concerned with a method for treating waste cellulosic fiber and paper mill sludge in a way to substantially neutralize the dioxin content and, at the same time, provide a finished material that has utility. The fiber product provided as a consequence of the method to be herein disclosed is substantially free of dioxins and is an environmentally safe, usable aggregate for cement fiber board and other applications. The term "neutralize" as applied to dioxins as used herein means destroying all active toxic or potentially toxic bacteria and tying up heavy metals by combining them with a cement or binder in a manner to eliminate the potential of such metals leaching into the environment.
Friberg, however, is not concerned with the neutralization of dioxins. In fact, Friberg includes the addition of calcium chloride to his second intermediate mixture. This results in the antithesis of an end product in which toxins are substantially neutralized, as the major carrier of toxins in paper fibers, such as paper mill sludge, is in the form of chlorine dioxide. Friberg's introduction of calcium chloride in this method works, if anything, to hinder not help detoxification.
Applicant discloses and claims herein a new continuous flow process for treating waste cellulosic fiber sludge which is extremely energy efficient, which requires no significant time and storage demands, and which, therefore, is commercially practicable for large scale implementation. In addition, the process herein described provides a finished product that is substantially free of dioxins as a consequence of neutralization of the dioxins in the manufacturing process and in which any remaining dioxins are firmly bound in aggregate material that substantially eliminates the possibility of such dioxins leaching out or otherwise becoming a pollutant.